选择题 . The Hypertext Transfer Protocol, the Web's ______ protocol, is at the heart of the WeB. HTTP is implemented in two programs: a ______ program and a server program. The client program and server program, executing on different end systems, talk to each other by ______ HTTP messages. HTTP defines how Web clients request Web pages from servers and how servers transfer Web pages to clients. When a user ______ a Web page, the browser sends HTTP request messages for the objects in the page to the server. The server ______ the requests and responds with HTTP response messages that contain the objects.71.

A、 transport-layer
B、 application-layer
C、 network-layer
D、 link-layer

【正确答案】 B

【答案解析】 Web的应用层协议超文本传输协议HTTP是Web的核心，它用于在两个程序中实现：客户端程序和服务器程序。运行在不同终端系统上的客户端程序和服务器程序通过交换HTTP消息来进行交互。HTTP定义了Web客户机如何从服务器请求Web页以及服务器如何将Web页传递给客户机。当用户请求一个Web页面时，浏览器将页面对象的HTTP请求发送到服务器，服务器接收请求并用包含对象的HTTP消息进行响应。